Gravity and magnetic methods - Geophysics for the Mineral Exploration Geoscientist - page 123

g) h)

0 5

Kilometres

5

8

6

8

i)

Figure 3.28 (cont.)

simplify the response are mostly applicable to magnetic
data. The aim is to transform the dipolar response charac-
teristic of mid-latitudes to the simpler monopole response
occurring at the poles ( Fig. 3.8 ) . Filters enhancing detail
emphasise responses from shallow depths by enhancing
their short-wavelength responses. Both wavelength and
gradient

the body is magnetism is vertical, the resultant anomaly can

be difficult to relate to the geometry of its source. Fortu-
nately for the interpreter, the problem is addressed by two
processing operations: the reduction-to-pole (RTP) and
the pseudogravity (PSG) transforms. Both are forms of
anomaly simplifier making magnetic data much easier to
analyse and allowing comparisons of data from different
magnetic latitudes.

'

filters are commonly used and allow structure to
be mapped in considerably more detail than in the '

data. The long-wavelength responses of large and deep-
seated features can also be enhanced using wavelength
filters.

' raw

3.7.2.1 Reduction-to-pole
The reduction-to-pole operator transforms magnetic
anomalies resulting from the inclined magnetism of non-
polar regions into their equivalent polar response where a
body

3.7.2 Reduction-to-pole and pseudogravity
transforms

is magnetism is vertical; compare Figs. 3.26a and d .
Polar magnetic anomalies resemble gravity anomalies in
that they are monopolar and occur directly above their
source, but with the advantage of being more localised to
the source than gravity anomalies. The resolution of close-
spaced sources is improved. Derivative enhancements are

'

As shown in Figs. 3.25a and 3.26a , magnetic responses are
much more complex than gravity responses, owing to the
dipolar nature of magnetism and the possibility that the
magnetisation of the body can be in any direction. Unless